Inflammation is an essential host response to control invading microbes and heal damaged tissues. Uncontrolled and persistent inflammation causes tissue injury in a plethora of inflammatory disorders. Neutrophils are the predominant leukocytes in acute inflammation. During infections neutrophils generate neutrophil extracellular traps (NETs), lattices of DNA-filaments decorated with toxic histones and enzymes that immobilize and neutralize bacteria. The relevance of NETs in host defense is illustrated by the fact that extracellular DNases serve as virulence factors in several pathogenic bacteria. However, inappropriately released NETs may harm host cells due to their cytotoxic, proinflammatory, and prothrombotic activity. Indeed, NETs are frequently associated with inflammatory or ischemic organ damage and the therapeutic infusion of DNases limits host injury in various animal models.
Extracellular trap (ET) formation is not limited to neutrophils as other leukocytes, namely monocytes, macrophages, basophils, eosinophils, and mast cells release ETs as well. Furthermore, cancer cells, including acute promyelocytic leukemia (APL) cells, and injured endothelial cells can expose DNA-filaments, which have ET-like features.
How the host degrades NETs in vivo to limit tissue damage during episodes of inflammation is poorly understood. DNase1 (D1) in serum has been shown to digest the DNA-backbone of NETs in vitro. Other extracellular DNases have been identified, including DNase1-like 3 (D1L3) in circulation, which can digest extracellular microparticle-associated chromatin.
D1 and D1L3 form along with DNase1-like 1 (D1L1) and DNase1-like 2 (D1L2) the DNase1-protein family, a group of homologous secreted DNase enzymes that are expressed in humans and provide drug candidates for NET-associated diseases. However, the physical, enzymatic, and pharmacokinetic properties of these enzymes are not ideal for therapy.
The present invention provides engineered DNases, including DNase1-like 3 and DNase1, for therapy, including for preventing or treating vascular occlusions that can result from release of NETs during acute inflammatory episodes.